Some known pipe couplings have been designed which have no provision for axial restraint. Changes in circumstances may require such couplings to perform to a higher specification than that of the original design. This leads to a requirement for axial locking of the pipes to be added to the coupling. Attempts to envelope the existing coupling by an external gripping means have been expensive, clumsy, bulky and heavy and aesthetically unpleasing which is unacceptable in applications such as drainage pipes for buildings where the pipework is often visible.
There is a need for a self-contained anchoring device which can be employed with various different existing designs of pipe joining systems to enable the pipes to be axially restrained.
According to the present invention there is provided an anchoring device for a pipe coupling comprising an annular channel of generally U-shaped cross-section having a web portion with flanges projecting radially inwardly from the longitudinal ends of the web portion, and a frusto-conical gripping ring located in the channel, the outer edge of the gripping ring being located inside the web portion of the annular channel adjacent one of the radially inwardly projecting flanges, the inner edge of the gripping ring being adjacent the other radially inwardly projecting flange and projecting radially inwardly beyond the said other flange, the annular channel being compressible circumferentially so that when the anchoring device is placed around a pipe of appropriate size and the annular channel is compressed, the inner edge of the frusto-conical gripping ring engages the outer surface of the pipe.
The annular gripping ring of the present invention provides a self-contained means for gripping a pipe. It is independent of the other prime function of a pipe joint, namely sealing. It will resist end load and will resist internal pressure.
Most known pipe couplings which have axial restraint are in the form of a cast iron or sheet metal housing with a flange at 90° to the pipe surface which either itself engages a corresponding groove or shoulder on the pipe surface or provides a surface against which an anchoring device is placed that will grip the pipe end surface. In either case, the strength of the material of the housing is critical in determining the strength of the actual restraint. Thus, in many cases, the known clamping device can be disproportionately bulky in relation to the pipework it connects.
In the present invention, the forces generated by the axial restraint system where the gripping ring engages the pipe on its inner periphery and is supported by the flange and web portion on its outer periphery are entirely contained by the channelled ring which encapsulates the gripping ring except on the inside of the channel where the channel is open to allow the inner edge of the gripping ring to project out of the channel to grip the pipe surface.
An anchoring device according to the invention may be used, for example, in conjunction with lightweight pipe joining clamps previously designed purely for gravity applications such as drainage pipes to convert them into a system capable of withstanding working pressures such as 16 bar and test pressures up to 64 bar. Jointing systems such as push-fit spigot and socket systems can now be converted to axial restraint systems by means of a simple sheet metal clamp that contains an anchoring device in accordance with the invention. Previously, it would have been necessary to cut off the ends of the pipe to enable a straight plain ended connector to be used, or to have a special clamp substantially larger than the profile of the push-fit joint that would clamp over the top and hold the pipes in place. Due to the bulk and varying length of such systems, a simple conversion of such pipe joints from non-restrained to restrained across a range of pipe diameters required by the piping industry has proved impossible in an economically viable way.
Preferably, the annular channel is an incomplete ring. The interior diameter of the web portion of the annular channel is smaller than the external diameter of the gripping ring in the unstressed condition so that the gripping ring is a tight fit in the channel. The annular channel has a circumferential gap so as to allow it to be compressed in use in order to allow the inner edge of the gripping ring to engage the pipe. The internal radial height of the flanges from the web portion is less than the overall width of the gripping ring measured in the radial direction so that the gripping ring projects inwardly beyond the flanges.
The inner edge of the gripping ring may be formed with a series of teeth to bite into the outer surface of the pipe when the ring is compressed. The gripping ring may extend more than 360° around the axis of the anchoring device so that the ends of the gripping ring overlap. The teeth may be flat in the conical plane of the gripping ring so as not to interfere with one another where they overlap when the anchoring device is compressed.
The anchoring device may be fitted into any suitable clamping device which fits over the pipe coupling. When the clamping device is tightened, the gap in the annular channel is reduced tightening the gripping ring around the pipe and causing it to engage the pipe surface.
When pressure is applied to the pipes, either in the form of a dead weight or by hydrostatic pressure, the pipe attempts to pull from the fitting causing the gripping ring to attempt to rotate or flatten inside the annular channel. It has been found that such rotational or flattening forces may easily be resisted by conventional clamping means used for clamping pipes intended for use in gravity pipe systems.